The present invention relates to a battery, a method of forming a battery cell container, and an electronic device.
In recent years, portable devices, represented by digital cameras and mobile phones, have been widely popularized. With popularization of various portable devices, their performances also have been rapidly improved. With additions of various functions, power consumption of a portable device has been gradually increased, as well. Therefore, it becomes a widely concerned subject in the industry on how to improve the electricity storage capacity of a battery to enable a portable device to have extended standby time.
At present, a battery of a general portable device commonly adopts a following structure. With a polymer lithium-ion secondary battery as an example, a positive electrode is formed by laying a layer of active materials consisting of LiCoO2 and zinc on a positive electrode collector made of aluminum foil. A negative electrode is formed by laying a layer of active materials consisting of, for example, carbon, coke, graphite and the like, on a negative electrode collector. By inserting one porous-film separator composed of polypropylene or polyethylene between the negative and the positive collectors, and filling polymer gel electrolyte between the electrodes and the separator, thus a sandwich-like battery cell is formed. Through encapsulating the battery cell with a container, a battery pack is formed.
As to the methods of forming the above-mentioned container, for example, a method in a first existing way recorded in CN1253387A is commonly adopted. FIG. 1(a) and FIG. 1(b) are schematic views of the molding method of a battery cell container in the first existing way. As shown in FIG. 1, a rectangular sheet-like substrate is evenly divided into a region 3a for forming a container main body and a region 3b for covering a battery cell accommodated in the container. In the region 3a, a cuboid battery cell container 6 is formed by a compression molding method. By mounting a battery cell (not shown) in the container 6, and folding the region 3b toward the region 3a side, thereby covering the battery cell, thus the encapsulation of the container is completed.
In the above-described method of vertically forming a cuboid container on a rectangular sheet-like substrate, the sheet-like substrate is generally a laminated thin film composed of, for example, a polypropylene layer, an aluminum layer and a nylon layer. As shown in the schematic views of FIG. 2, when the thin film-like substrate is fixed and stretched by a stretching head (a metal mold) such as a stamping head or the like, since the ductility of the substrate itself has a certain limit (in particular, the aluminum layer therein), and there exists a great frictional force between the metal mold and the substrate as shown in FIG. 2(c), therefore, during the formation of the container, there exist such a case that the thin film-like substrate is stretched only at local parts (such as the substrate part at both sides of the metal mold conducting the stretching), as a result, there inevitably exists a certain physical limit to the stretching depth (molding depth). Consequently, it becomes a difficult problem to improve the molding depth on condition of not increasing material consumption.
In order to solve the above problem, a method in a second existing way is proposed. FIG. 3(a) and FIG. 3(b) are schematic views of the molding method of a battery cell container in the second existing way. As shown in FIG. 3(a) and FIG. 3(b), the method comprises: dividing one container originally formed on the sheet-like substrate into two portions, and molding the two container portions by vertically stretching on the sheet-like substrate, then folding to form a battery cell container. In this method, through dividing a container into two portions to be stretched, it solves to a certain extent, the problem that the molding depth is limited since the stretching limit exists. However, as shown in FIG. 2, in the case of stretching two container portions, because the material of the substrate part between the two container portions will also be stretched and hence used for molding parts of the walls of the two container portions, thus to some extent, the stretching limit is suppressed. Although it is possible to solve such problem by widening the width of the substrate part between the two container portions, it will bring a problem of material loss.
In addition, a method in a third existing way is disclosed in Japanese laid-open publication No. 2004-31194. FIG. 4 is a schematic view of the molding method of a battery cell container in the third existing way. As shown in FIG. 4, the method comprises: forming two container portions on two sheet-like substrates, respectively, and then oohering them together. In that invention, because the two container portions are respectively formed on two sheet-like substrates and then cohere together, there exists difficulties in positioning of the two container portions, moreover, the volume energy density is reduced due to the added sheet-like substrate part.